Re: [math-fun] natural numbers

On Mar 3, 2015, at 10:04 AM, Mike Speciner <ms@alum.mit.edu> wrote:

Interesting. I use Z with a positive integer subscript n for Z/nZ, and with an appended asterisk for the multiplicative group of integers mod n relatively prime to n.

In non-number theory discussions, I prefer to do this, too. But many number theorists see Z_p (mainly for p prime) as the notation for the p-adic integers. So in those contexts I use Z/nZ (n prime or not) for the group or ring of integers mod n. When typography permits I prefer to denote the multiplicative group by adding an × superscript. (That's supposed to be a multiplication symbol.) PUZZLE: Find the n for which the invertible elements of Z/nZ are all square roots of unity. --Dan